Power supply apparatus

ABSTRACT

The power supply apparatus ( 10 ) comprises an input ( 12 ), first and second outputs ( 14, 16 ) and means ( 18 ) for conversion of the electric current which are connected between the input ( 12 ) and the outputs ( 14, 16 ).  
     The conversion means ( 18 ) comprise a transformer ( 20 ) comprising a primary winding ( 20 A) supplied by the input electric current and first and second secondary windings ( 20 B,  20 C) respectively supplying the first and second outputs ( 14, 16 ) by way of first and second shaping circuits ( 22, 24 ). The first shaping circuit ( 22 ) comprises regulating means ( 48 ) adapted to act on the electric current feeding the primary winding ( 20 A). The regulating means ( 48 ) are adapted to effect regulation in dependence on a signal from the first shaping circuit ( 22 ). The second shaping circuit ( 24 ) comprises autonomous means ( 86, 88 ) for regulating the current provided by the second output ( 16 ).

[0001] The present invention concerns a power supply apparatus intendedin particular to be used in an aircraft, It concerns more particularly apower supply apparatus of the type comprising:

[0002] an input for receiving an input electric current;

[0003] first and second outputs for providing first and second electricpower supply currents each having specific characteristics; and

[0004] means for conversion of the electric current connected betweensaid input and said first and second outputs.

[0005] It is nowadays necessary in aircraft cabins to supply electricalenergy to different operational members which are available topassengers. Those operational members are formed for example by videoscreens, lamps, power supply sockets for portable computers as well aselectrical actuators which are fitted in the seats in order to ensureindependent displacement of different movable components of the seat.

[0006] Those operational members are supplied with power from theelectric power distribution system of the aircraft, which conventionallydelivers an alternating current at 115 volts, at a frequency of 400 Hz.

[0007] Numerous operational members require a power supply withalternating current at 110 volts, at a frequency of 60 Hz for theiroperation. On the other hand, for safety reasons, other operationalmembers such as the motors of the actuators which are fitted in theseats are direct-current devices. Their power supply voltage isgenerally 12 or 24 volts.

[0008] It is known to connect to the electric power distribution systeminstalled in the aircraft a converter for implementing conversion of thealternating current into direct current. To supply alternating currentto the operational members requiring such a power supply anotherconverter is used. That provides for conversion of the distributedalternating current into an alternating current of different voltage andfrequency.

[0009] Thus, the known solution involves using a .plurality ofconverters each incorporating a transformer. Those converters are eachconnected to the electric power distribution system of the aircraft.That power supply architecture is relatively bulky and increases thetotal weight involved in the power supply.

[0010] The object of the invention is to propose a power supplyapparatus of reduced bulk and weight, which makes it possible to supplypower to a plurality of types of operational members from electriccurrents of different characteristics

[0011] For that purpose the invention concerns a power supply apparatusof the above-mentioned type, in which said conversion means comprise atransformer comprising a primary winding supplied by the input electriccurrent and first and second secondary windings respectively feeding thefirst and second outputs by way of first and second shaping circuits,the primary winding and the first and second secondary windings beingdisposed on the same magnetic circuit, the first shaping circuitcomprising regulating means adapted to act on the electric currentsupplying the primary winding, which regulating means are adapted toensure regulation in dependence on a signal from the first shapingcircuit, and the second shaping circuit comprising autonomous means forregulation of the current produced by the second output, said secondshaping circuit being adapted to produce an alternating current; and thesecond shaping circuit comprising a rectification stage and, at theoutput of said rectification stage, means for modifying the voltage inaccordance with a variable division ratio:

[0012] In accordance with particular embodiments the apparatus comprisesone or more of the following features:

[0013] said first shaping circuit is adapted to produce a directcurrent;

[0014] said means for modifying the voltage in accordance with avariable division ratio comprise a regulator for the output voltage ofsaid means for modifying the voltage in accordance with a variabledivision ratio and means for controlling said regulator on the basis ofa variable control voltage;

[0015] said means for controlling a variable control voltage comprise avariable-ratio voltage divider bridge connected at the output of saidmeans for modifying the voltage in accordance with a variable divisionratio;

[0016] said second shaping circuit comprises at the output of said meansfor modifying the voltage in accordance with a variable division ratioan inverter bridge controlled at a predetermined frequency; and

[0017] said means for modifying the voltage in accordance with avariable division ratio are adapted to produce a periodic signal of afrequency double the alternating current produced at the output of thesecond shaping circuit.

[0018] The invention also relates to a method of converting an electriccurrent from an input of a power supply apparatus receiving an inputelectric current, to first and second output electric currents eachhaving specific characteristics.

[0019] The invention will be better appreciated from the description setforth hereinafter solely by way of example and with reference to thesingle FIGURE which is a diagrammatic view of a power supply apparatusaccording to the invention.

[0020] The power supply apparatus 10 illustrated in FIG. 1 is intendedto be installed in an aircraft. It comprises an input 12 for receivingan input electric current. That input is intended to be connected to theelectrical energy distribution system of the aircraft. That systemprovides for example an alternating current at a voltage of 115 voltsand at a frequency of 400 Hz.

[0021] The power supply apparatus 10 further comprises two outputs. Afirst output 16 is adapted to supply loads such as electrical actuatorswith a 24 volt dc voltage. The second output 16 is adapted to supplyloads such as video screens with an ac voltage at 110 volts at afrequency of 60 Hz Means 18 for conversion of the electric current areinterposed between the input 12 and the first and second outputs 14 and16.

[0022] The conversion means 18 comprise a single transformer 20comprising a primary winding 20A and two secondary windings 20B, 20C.Those secondary windings 20B, 20C respectively supply the outputs 14 and16 by way of shaping circuits respectively identified at 22 and 24.

[0023] The first shaping circuit 22 comprises regulating means 26 actingon the current supplying the primary winding 20A of the transformer. Theregulating means 26 are adapted to ensure regulation in dependence onthe signal from the first shaping circuit and in particular its output14.

[0024] The second shaping circuit 24 comprises autonomous regulatingmeans which are specific to that shaping circuit.

[0025] The transformer 20 is for example a direct transformer, generallyreferred to as a ‘forward transformer’.

[0026] The primary winding 20A of the transformer is connected to theoutput terminals of a shape factor corrector 30 which is supplied fromthe input 12 of the apparatus.

[0027] The shape factor corrector 30 is intended to bring into phase thestrength and the voltage supplied by the electrical distribution systemand to convert the alternating current of the system Into a directcurrent whose voltage is equal to 225 V.

[0028] A switching member 32 is disposed between the primary winding 20Aand the output of the shape factor corrector 30 in order to selectivelycontrol the feed to the primary winding 20A from the shape factorcorrector 30.

[0029] In addition, and as is known per se, the transformer 20 comprisesa demagnetisation winding 20D connected in parallel by way of a diode 34with the output terminals of the shape factor corrector.

[0030] The shaping circuit 22 comprises a rectification stage 40 formedby two diodes connected in series and in opposite relationship acrossthe terminals of the first secondary winding 20B. One of the terminalsof the first secondary winding 20B is connected to earth.

[0031] A filtering cell 42 is connected at the output of therectification stage 40. The filtering cell 42 is formed by a winding 44and a capacitor 46 which are connected in series and connected betweenthe output of the rectification stage formed between the two diodes andearth.

[0032] The first output 14 is formed at the terminals of the capacitor46.

[0033] The regulating means 26 comprise a regulator 48 of conventionaltype such as a pulse width modulation regulator (PWM). The input of theregulator 48 is connected to the terminals of the first output 14.

[0034] The output of the regulator 48 is connected to the controlterminal of the switching member 32 in order to ensure selectiveconnection of the primary winding 20A to the output of the shape factorcorrector 30. The control frequency of the switching member 32 which isimposed by the regulator 48 is for example 170 kHz.

[0035] The primary winding 20A and the first secondary winding 20B ofthe transformer are dimensioned and the regulator 48 is adapted in sucha way that the voltage across the terminals of the first output 14 isequal to 24 volts, The transformer then operates with a cycle ratio of40%.

[0036] The second shaping circuit 24 is connected to the output of thesecond secondary winding 20C of the transformer. The circuit 24 furthercomprises at its input a rectification stage 50 similar to the stage 40of the first circuit 22. The rectification stage 50 thus comprises twodiodes connected in series and in opposite relationship across theterminals of the second secondary winding 20C.

[0037] A filtering cell 52 is provided at the output of therectification stage 50. The filtering cell 52, like the cell 42, isformed by a coil 54 and a capacitor 56 which are connected in seriesbetween ground and the central point of the two diodes. The filteringcell 52 is adapted to smooth the voltage produced at the output of therectification stage 50.

[0038] The primary winding 20A and the second secondary winding 20C ofthe transformer as well as the elements of the filtering cell 52 areadapted to produce at the terminals of the capacitor 56 a dc voltage ofsubstantially 180 volts.

[0039] A stage 70 for reducing the voltage in accordance with a variabledivision ratio is connected at the output of the rectification stage 50and the filtering cell 52.

[0040] The stage 70 comprises at its input a switching member 72 ofwhich one terminal is connected between the coil 54 and the capacitor56. It further comprises a freewheel diode 74 connected between groundand the other terminal of the switching member 72. An energy storagecoil 76 is connected to that same terminal of the switching member 72. Afilter capacitor 78 connects the other terminal of the storage coil 76to ground,

[0041] The output of the voltage reduction stage 70 is defined betweenground and the connecting point of the coil 76 and the capacitor 78.

[0042] The regulating means 28 specific to the second shaping circuit 24provide for a reduction in voltage in accordance with a variabledivision ratio, this being effected cyclically.

[0043] In particular the regulation action is adapted to reduce thevoltage of 180 volts in accordance with a sinusoidal law so as toreconstitute at the output the positive parts of the sine curve wantedat the output but at a frequency of 120 Hz.

[0044] In order to ensure that progressive reduction in voltage theregulating means comprise a regulator 86 of pulse width modulation type(PWM). The output of the regulator 86 is connected to the controlterminal of the switching member 72. The chopping frequency supplied bythe regulator 86 is sufficiently high to be effectively filtered. It isfor example fixed at 100 kHz. The input of the regulator 86 is connectedto the center point of a variable-ratio voltage divider bridge 88.

[0045] The voltage divider bridge 88 comprises a measuring resistor 90of which a first terminal is connected between the filtering capacitor78 and the energy storage coil 76. The measuring resistor 90 isconnected in series with a complementary resistive module of the voltagedivider bridge whose resistance is variable in controlled fashion. Thatmodule is formed by an array of eight resistors 92 each connected inseries with an individually controllable switching member 94. The armswhich are formed in that way of a resistance arrangement in series witha switching member are connected in parallel between the second terminalof the measuring resistor 90 and ground.

[0046] In the illustrated example eight branches comprising a resistanceare used. That number however may differ in dependence on the purity ofthe alternating signal that is wanted.

[0047] The control terminal of each of the switching members 94 isconnected to its own output of a pilot control device 100 such as amicrocontroller.

[0048] The pilot control device 100 is adapted for cyclic control of theswitching members 94.

[0049] The repetition rate of the control signal which is applied to theswitching members is equal to double the frequency of the alternatingsignal that is wanted at the output 16, namely 120 Hz.

[0050] The choice of the values of the resistors is such that the lawfor attenuation of the voltage in dependence on time which is imposed bythe regulator 86 is homothetic of the function att(x)=1/sin(2πFx) inwhich F is double the frequency of the alternating signal to begenerated at the output 16, namely 120 Hz in the example beingconsidered, and x is time.

[0051] Quantification of the function att(x) is effected in such a wayas to afford a good approximation to that function. It can be generateddigitally by the microcontroller delivering control signals to theswitching members 94 which are sequenced in respect of time in cyclicfashion.

[0052] The time interval between two successive switching operations inthe resistive module is equal to the period of the sine curve to begenerated, namely {fraction (1/60)}th of a Hz, divided by 32, if thesuccessive time intervals are all identical. In an alternativeconfiguration control by a variation in that time interval is effectedto improve the level of precision of quantification of the attenuationlaw.

[0053] For example, in the case of a control involving a regularinterval and with a reference voltage of 2.5 volts the followingattenuation effects are obtained if TO represents the zero-crossing ofthe output sine curve. T0 + 520 T0 + 1042 T0 +1563 T0 + 2083 T0 + 2604T0 + 3125 T0 + 3646 T0 μs μs μs μs μs μs μs 1 0.0825 0.0419 0.02890.0227 0.0193 0.0174 0.0164

[0054] A low pass filter 102 is disposed between the control input ofthe regulator 86 and the center point of the voltage divider bridge 88.That filter is adapted to eliminate the spectral components due tofolding of the spectrum in the vicinity of the sampling frequency, thatis to say thirty two times 60 Hz, that is to say 1920 Hz, in the examplebeing considered here. That filtering frequency is taken as being equalfor example to substantially ten times the frequency of the sinusoidalsignal, that is to say about 500 Hz.

[0055] Finally the input terminals of a controlled inverter bridge 120are connected at the output of the voltage reduction stage 70, that isto say to the terminals of the filtering capacitor 76. The terminals ofthe second output 16 are formed by the output terminals of thecontrolled inverter bridge 120.

[0056] On each of its four arms the inverter bridge 120 comprises aswitching member 122 controlled in dependence on a control signal. Thatcontrol signal which is produced by any suitable device is a logicsignal synchronised with the arches of the desired sine curve. Thefrequency of that control signal is 120 Hz. It is advantageouslygenerated by the microcontroller forming the pilot control device 100 ofthe divider bridge.

[0057] In operation of the power supply arrangement the conduction timeof the switching member 32 is regulated in dependence on the voltage atthe first output 14 of the apparatus.

[0058] Thus, regulation applied upstream of the transformer is ensuredonly in dependence on the output 14 supplying a dc voltage.

[0059] On the other hand, for alternating operation, regulation iseffected only within the shaping circuit 24. That regulation isindependent of the regulation implemented upstream of the transformer bythe first regulating means 26.

[0060] In the course of a cycle the pilot control device 100 effectsprogressive switching of the different switching members 94 integratedinto the voltage divider bridge 88 in order to modify the voltageapplied at the input of the regulator 86. Thus, the width of the pulsesproduced upon closure of the switching member 72 under the control ofthe regulator 86 is proportional to the difference between the imposedreference which is fixed for example at 2.5 volts and the image of thesinusoidal signal attenuated by the law att(x). The gain of theregulator 86 is selected to be sufficiently high for that difference toremain small.

[0061] Thus, a signal formed by a succession of positive sinusoidalarches is obtained at the output of the voltage reduction stage 70. Itsfrequency is 120 Hz. That signal is subject to the sine law produceddigitally by the successive switching operations of the switchingmembers.

[0062] In dependence on imperfections in the circuits used, theattenuation law att(x) can be corrected in order to improve the spectralpurity of the synthesised sinusoidal signal. It is possible for exampleto correct delays in propagation, asymmetries in the output bridge andlinearity defects.

[0063] The signal obtained at the output of the voltage reduction stage70 is formed by a succession of positive sine wave arches.

[0064] The controlled inverter bridge 120 provides for inversion of onesine wave arch out of two, thus resulting in making alternating thesignal supplied at the second output 16.

[0065] Inversion of the signal is effected at the zero-crossing of thesynthesised sinusoidal signal.

[0066] Thus the solution proposed for the power supply to produce dcvoltage and ac voltage from the alternating current from thedistribution system makes it possible to use only a single transformerin which the two secondary windings are installed on the same magneticcircuit, being excited by the primary winding which is powered from theelectrical distribution system.

[0067] The sinusoidal signal is generated by synthesis from a continuoussignal formed at the output of the transformer.

[0068] As generation of power is effected by high-frequency chopping thecircuits used are of small bulk and low weight which are compatible withan aeronautical environment. Indeed, direct conversion of the frequencyof the distribution system to a frequency of 60 Hz would entail the useof bulky components which are difficult to render compatible withaircraft constraints.

[0069] The control arrangements used both for the direct current and forthe alternating current permit very stable output voltages andfrequencies, irrespective of the load, the latter being capable ofvarying very substantially.

[0070] Moreover, generation of the sinusoidal signal being effecteddigitally, it can be corrected in respect of imperfections in thecircuits used, thus improving the output performances from the point ofview of the rate of harmonic distortion.

[0071] Finally, generation of the sinusoidal signal being synthesisedunder the pilot control of a microcontroller, the power supply apparatuscan be easily modified by a simple change in the control parameters ofthe microcontroller or by a modification in only some components such asthe resistors 92.

[0072] In particular the ac voltage can be reduced to 100 volts insteadof 110 volts and the frequency can be changed from 60 Hz to 50 Hz.

What is claimed is
 1. A power supply apparatus comprising: an input forreceiving an input electric current; first and second outputs forproviding first and second electric power supply currents each havingspecific characteristics; and means for conversion of the electriccurrent connected between said input and said first and second outputssaid conversion means comprising a transformer comprising a primarywinding supplied by said input electric current and first and secondsecondary windings respectively feeding said first and second outputs byway of first and second shaping circuits, said primary winding and saidfirst and second secondary windings being disposed on the same magneticcircuit, said first shaping circuit comprising regulating means adaptedto act on the electric current supplying said primary winding, saidregulating means being adapted to ensure regulation in dependence on asignal from said first shaping circuit, said second shaping circuitcomprising autonomous means for regulation of the current produced bysaid second output, said second shaping circuit being adapted to providean alternating current, and said second shaping circuit comprising arectification stage and, at the output of said rectification stage,means for modifying the voltage in accordance with a variable divisionratio.
 2. Apparatus as set forth in claim 1, wherein said first shapingcircuit is adapted to provide a direct current.
 3. Apparatus as setforth in claim 1 wherein said modifying means for modifying the voltagein accordance with a variable division ratio comprise a regulator forthe output voltage of said modifying means and control means forcontrolling said regulator on the basis of a variable control voltage.4. Apparatus as set forth in claim 3, wherein said control means forcontrolling a variable control voltage comprise a variable-ratio voltagedivider bridge connected at the output of said modifying means formodifying the voltage in accordance with a variable division ratio. 5.Apparatus as set forth in claim 1, wherein at the output of saidmodifying means for modifying the voltage in accordance with a variabledivision ratio, said second shaping circuit comprises an inverter bridgecontrolled at a predetermined frequency.
 6. Apparatus as set forth inclaim 1, wherein said modifying means for modifying the voltage inaccordance with a variable division ratio, are adapted to produce aperiodic signal at a frequency double the alternating current providedat said output of said second shaping circuit